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Silicon dioxide (SiO2) is deposited at between 300 and 450C (depending on needs... ie metals 300C), low pressure (~350 mtorr), from silane and oxygen with or without phosphine doping. Doped LTO is also called PSG, or phosphosilicate glass). The refractive index of the film depends on the phosphorous content, lower deposition rate. The refractive index is also influenced by the temperature of the deposition. The oxide deposition rate is mostly dependent on the temperature and is ~ 175A/min at 400C for 4 inch wafers (~200A/min for 3 inch wafers).

Operating Procedure

Basic Operation Instructions

  1. Clean substrates
    Diffusion clean with HF last
  2. Enable the furnace
  3. Verify Pump program running
    Go to the furnace and use the STATUS button to verify that the system is in 'RUN' mode and running the "PUMP program."
  4. End Pump program
    ALARM ACK twice
  5. Verify the Tube is vented
    Ten minutes after the pump program has ended you must manually test that the tube is vented. Push MANUAL on the boat puller, push FAST, then LOOK AT THE TUBE while you hold down OUT. You should immediately see the boat start to come out. If it does not, stop and wait 10 more minutes and test it again.
  6. Load your program (only after verifying manually that tube is vented)
    From TYCOM type "LO  <program name>  <furnace#>" <RET>.  You will be asked to enter the deposit time.
  7. Run program
  8. Load your wafers.
    The first boat (as the boats come out of the furnace) is for dummies. The second boat is the clean non-metal boat.  The third boat is the metal boat.  The fourth boat (the last one to come out of the tube) is a dummy boat.  Both dummy boats should have 4 to 6 wafers.  The two middle boats should have 13 wafers each.
  9. Send in tube
    ALARM ACK once
  10. Monitor furnace
    Take pressure readings during the gross leak check, leak check and the deposition steps of the program and write the values in the logbook.
  11. Unload wafers
  12. End program
    ALARM ACK twice
  13. Load pump program
  14. Run Pump program
  15. Measure wafers and log results
  16. Disable the furnace


Process Monitoring and Machine Qualification

Each month, tool qualification runs are performed on most tools in the SNF to monitor variations in each tool’s performance. The purpose of the TylanBPSG qual is to monitor oxide thickness and uniformity both wafer-to-wafer over a 26 wafer load and within a wafer. The qual is performed by SUMO members, but users may perform the specified qual process before tool use if more recent qual data is desired for reference.

For more information on the SNF tool performance monitoring system and SUMO, please see the Monthly Tool Monitoring page under the Equipment tab on the SNF wiki.


Qual Process Overview

The TylanBPSG qual runs six new "L" test wafers through the LTO400PC for 20 minutes to be coated with 1,000A SiO2. After the deposition, the wafers are analyzed via Woollam using the nine point Silicon Oxide (100 - 10,000 Ang) analysis. 


  1. Use six new 'L' test wafers; <100>, P-type (boron), 10-20 ohm-cm.
  2. Scribe wafer numbers, and clean in piranha at wbclean_res-piranha.
  3. Clean at wbclean-1/2 in the following sequence; 5:1:1 H2O:H2O2:NH4OH ten minutes, rinse, 5:1:1 DI;HCl:H2O2 ten minutes, rinse, 50:1 DI:HF 30 sec, rinse, spin dry.

  4. Check pump program status, as specified in the Basic Operating Procedure above.
  5. Load program LTO400PC into TylanBPSG. Time variable is 00:20:00.
  6. The boats must be loaded with dummies (13 wafers in each, loaded every other slot) at all times to ensure uniform wafer to wafer deposition.
  7. Using very clean tweezers or vacuum wand replace the dummy wafers with cleaned test wafers in the following positions with flats up:
        • 1st boat (Front) in the 5th slot.
        • 1st boat in the 13th.
        • 1st boat in the 21st slot.
        • 2nd boat (Back) in the 5th slot.
        • 2nd boat in the 13th.
        • 2nd boat in the 21st slot.


    Post-Deposition Measurements

    1. Measure the thickness and index of refraction at 9 points across the wafer using Woollam program Silicon Oxide (100 - 10,000 Ang).
    2. Report the average thickness, standard deviation, and n at 633 nm for the wafer. Test sites should be no more than about 15mm from the edge of the wafer.


    Reported Data

    Qual data may also be found on the Badger comment log. The following data is reported for the TylanBPSG qual.

    • average deposition thickness
    • one standard deviation
    • index of refraction

    If test values are not within 10% of plotted test average, contact the Diffusion Process/Maintenance team. Save wafers in a box with the date, furnace number, program name and growth time.  They may be re-tested sometime in the future.


    Qualification Results 

    4-5-11 TylanBPSG qual

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